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By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0. 994916 fiddles created (11009 in the last week).

CREATE TABLE tab(a,b,c) AS values (1, 1, null), (2, null, null), (3, null, null), (4, null, 1), (6, null, null), (7, null, null), (8, 1, null), (9, null, 1), (10, 1,null), (11,null,1), (12,1,1);
11 rows affected
 hidden batch(es)


SELECT a,b,c, CASE WHEN b = 1 AND c= 1 THEN 1 WHEN b =1 THEN COUNT(*) OVER(PARTITION BY s)+1 END AS cnt FROM (SELECT *, SUM(COALESCE(b,0)+COALESCE(c,0)) OVER(ORDER BY a) s FROM tab) s
a b c cnt
1 1 4
2
3
4 1
6
7
8 1 2
9 1
10 1 2
11 1
12 1 1 1
 hidden batch(es)